The present invention relates to electrical signalling system and is more particularly concerned with a signalling system applicable to a high-speed data transmission system employing repeater stations along its route, and in which the data transmission is effected in a so-called disparity-displaying or self-checking form of digital coding over say coaxial cables constituting the transmission media.
In a system of this kind two main types of repeaters may be used namely (a) dependent repeaters which require to be fed with power over the transmission media and (b) so-called intermediate or power-feeding repeaters which have integral power supplies and which in conjunction with terminal station equipments provide the electrical power-supplies for the whole system.
One form of monitoring and status reporting in respect of a transmission system using dependent and power-feeding repeaters is disclosed in co-pending application Ser. No. 16141/71, and in that system the digital regenerator of each repeater of both types has an error detector individually associated with it and performing a continuous monitoring function as regards its output. Indeed this detector produces a fault status signal in the event of either of two conditions arising, namely (a) that the output of digital regenerator has ceased or (b) that an error-rate-limit has been reached in respect of digital-transmission code disparities. In the known system, status interrogation in respect of the whole system is effected from a particular end (terminal station) at regular intervals (typically 5 seconds) by an interrogate signal pulse developed there at these intervals and subjected to regeneration at each repeater involved and extended to its successor. The repeater, upon detecting an interrogate signal at a particular access path, is required to return a response signal (indicative of the prevailing status) to that access path for extension to the interrogating terminal station by any intervening repeaters; signal regeneration processes being employed at the repeaters involved. Regeneration of the interrogate signal pulse by a repeater is effected upon completion of the response signal sequence.
Also in the system of the co-pending Application, addition monitoring and status reporting facilities are provided at power-feeding repeaters in respect of salient points of the particular repeater stations. When an interrogate signal is received at such a repeater, an extended period of interrogation and reporting is developed for it, to permit the additional response signals to be developed and transmitted back to the interrogating terminal station, prior to the interrogate signal being regenerated to the next repeater.
An object of the present invention is to provide a supervisory system of the general kind outline but which offers improved facilities and enables more accurate interpretation of response signals to be effected.
According to the invention there is provided a repeater for a digital data-transmission system using a disparity-displaying digital code, and including a digital regenerator and error-detecting means therefor and characterised in that supervisory control means incorporated in the repeater is operative upon reception of an interrogate pulse signal, over one access path also used as a digital-data path, to cause a response signal to be returned over said access path according to the prevailing state of said error-detecting means, said response signal comprising a different number of pulses for each of the two possible output states of said error-detecting means.
According to the invention said repeater is the first of a pair of repeaters of a particular repeater station, both repeaters including at least substantially identical digital regenerators and error-detecting means, and being incorporated in different digital data-transmission paths, said repeaters being so interconnected that the reception of a said interrogate pulse signal by said first repeater is effective in that the aforesaid response signal also takes into account the prevailing state of the error-detecting means serving the digital regenerator of the second repeater.
Also according to the invention there is provided a digital-data line-transmission system comprising two repeated transmission paths between terminal stations, in which, at each repeater station of the system, a repeater of the kind referred to above is provided for each transmission path, and as a result of an interrogate pulse signal generated at one said terminal station and applied to one transmission path serving a corresponding repeater of each station the supervisory control means of each said repeater successively upon reception of an interrogate pulse is operative to return a response signal to its access path and to effect delayed regeneration of the received interrogate pulse signal to the succeeding repeater (if any) of said transmission path; the supervisory control means of each repeater also being controlled by reception of a response signal to regenerate that response signal and apply it to its access path.
The invention will be better understood from the following description of methods of carrying it into effect which should be read in conjunction with the accompanying drawings comprising FIGS. 1 through 6.